Modern communication architectures that utilize packet-based or cell-based methods such as Voice over IP (VoIP) or Voice over ATM (VoATM), for example, provide for separation of the connection control and the bearer channel control. The communication between one/a plurality of subscribers such as ISDN/PSTN subscribers, for example, routed via traditional circuit-switched telecommunication networks up to now, is then routed via IP networks. To continue to allow communication with traditional circuit-switched telecommunication networks such as PSTNs (Public Switched Telephone Networks), a “translation” between the two different transport technologies is required, which is performed in crosspoints. At such a crosspoint, the first transport technology for the payload information is converted into the second transport technology by using specific facilities designated as a Media Gateway (MG).
The Media Gateways themselves are controlled by central entities, the Media Gateway Controllers (MGC). The signaling information transmitted between two Media Gateway Controllers is transported, for example, by using a BICC protocol (Bearer Independent Call Control Protocol) or SIP/SIP-T protocol. The Media Gateway Controllers are essentially used for the coordination of the Media Gateways and monitor/control connections (bearer connections) between the Media Gateways. The control of the Media Gateways is effected, for example, with the aid of the MGCP (Media Gateway Controller Protocol) or the H.248 protocol.
In the case of packet-based connections, particularly in the case of connections routed via the IP network, the payload data stream is therefore routed direct between the subscribers or gateways involved outside the switching office. The legally prescribed possibility of tapping the payload data (Lawful Interception, LI), designated as LI for short in the following, is usually effected via a conventional interface outside the packet network, implemented in TDM technology. An outgoing call via the packet network with a pure audio connection from an A subscriber who has to be monitored is then tapped in a TDM loop. This means that a conversion to TDM must be performed first. There, the payload data is tapped, forwarded to the parties tasked in this respect (LEAs, Law Enforcement Agencies), designated as LEAs for short in the following, then converted back into an IP protocol and fed to the called subscriber (B subscriber).
The corresponding relationships are shown in FIG. 1. For the purposes of tapping the voice connections in the packet network, the data stream is routed via Media Gateways MG in a loop to the TDM network and back. In the TDM network, the data stream is tapped in the known manner.